I can still make the problem happen, but it is not consistent. It seems that clicking through a bunch of pages while in a translated version, then clicking the American flag, will sometimes leave all the links pointing to the translated pages even though the text is now back to English. I'll keep playing with it to see if I can understand why it happens only occasionally.

Have you ever seen this issue before? If so, maybe one of the other Joomla plugins is to blame.